1. Field of the Invention
This invention relates to solid-state voltage references. More particularly, this invention relates to improved means and methods for temperature-compensating such voltage references, and to simplified procedures by which such references may be set for optimum compensation performance.
2. Description of the Prior Art
Solid-state voltage references commonly incorporate a junction voltage source, such as a Zener, which exhibits a significant temperature coefficient requiring compensation. For many reference devices, the voltage-vs-temperature relationship can be approximated as: EQU V.sub.dev =V.sub.K +.alpha.(T-T.sub.K) Eq. 1
where V.sub.dev is the device terminal voltage at any temperture T, V.sub.K and T.sub.K are constants, and .alpha. is a coefficient which varies with the processing of the device.
To provide compensation for the changes in voltage with temperature, the output of such a device can be summed with a compensating voltage circuit, such as a band-gap junction source, having a temperature coefficient opposite to the original in sign (slope), and incorporating appropriate scaling to develop the specified output voltage level. The characteristics of such a compensated voltage reference device may be represented by the following relationship: EQU V.sub.ref =.lambda.[(V.sub.GO -.beta.T).sigma.+V.sub.K +.alpha.(T-T.sub.K)]Eq. 2
where V.sub.GO is the band-gap voltage, .beta. is the temperature coefficient of a forward-biased junction, .sigma. is a proportionality factor between the voltage reference device and the compensating device, and .lambda. is an overall scaling factor needed to achieve a specified voltage value.
Such a device has two degrees of freedom for adjustment purposes, represented symbolically by .sigma. (slope) and .lambda. (scaling) in Equation (2) above. One procedure in adjusting the device for specified operating characteristics is to utilize a computer-operated algorithm to set .sigma. at the proper value to minimize temperature-induced variations for a calculated value of .alpha., and then adjust .lambda. to achieve the specified output voltage V.sub.ref'. This procedure accordingly requires two separate adjustment steps, one for each of the two degrees of freedom of the control circuit design. Experience has shown however that this procedure is undesirably complex and expensive to carry out, and although useful commercially, it is not fully satisfactory in achieving desired performance. Thus a need for significant improvement has become evident.